Punching apparatus and method

ABSTRACT

A punching apparatus includes a plurality of punches for punching a workpiece, a pad, and a single piston supporting the pad. The punches are disposed on a top surface of a portion of the pad. The top surface has a circumference circumscribing circumferences of outermost ones of the punches. A diameter of the piston is larger than a diameter of the portion of the pad.

FIELD OF THE INVENTION

The present invention relates to a punching apparatus and method for punching a workpiece.

BACKGROUND OF THE INVENTION

A workpiece-punching apparatus includes a plurality of punches for punching a workpiece or metal sheet, a pad supporting the punches, and a shaft for moving the pad between an advanced position and a retracted position, as disclosed in JP-A-11-254190.

FIG. 8 hereof shows a workpiece-punching apparatus 101 disclosed in JP-A-11-254190. The punching apparatus 101 includes a table 102 and a bolster 103 provided on the table 102. The bolster 103 has a pad 105 vertically movably provided in an upper part thereof for supporting a plurality of punches 104. The pad 105 is fastened to a nut 106 of a ball screw. The ball screw includes a threaded shaft 107 rotationally provided in the upper part of the bolster 103. The shaft 107 engages the nut 106 with balls 108 being disposed in a groove formed between the shaft 107 and the nut 108. Rotation of the shaft 107 causes the pad 105 and the punches 104 to move up and down together.

The bolster 103 has a die 109 provided at a lower part thereof. On the die 109, a metal sheet 110 is set. The plurality of the punches 104 is moved down to punch the metal sheet 110 to form a plurality of products of predetermined shapes.

The product may be each required to have a thickness accuracy. In order to provide products each having the accurate thickness, it is necessary to evenly move the plurality of the punches 104 downward.

As for the punching apparatus 101, since a diameter D1 of the shaft 107 is smaller than a diameter D2 of the pad 105, an outer portion of the pad 105 is undesirably flexed on a fulcrum defined by a central portion of the pad 105 located directly below the shaft 107, under loads applied to the punches 104 when the metal sheet 110 is punched. That is, when the metal sheet 110 is punched to form products, loads are not evenly applied to a vicinity of the central portion of the pad 105 and a vicinity of the outer portion of the pad 105. This would result in variation in thickness accuracy between the formed products.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a technique for punching a workpiece to form a plurality of products each having an enhanced thickness accuracy.

According to one aspect of the present invention, there is provided a punching apparatus comprising: a plurality of punches for punching a workpiece; a pad; and a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position; wherein the pad is supported on the driving mechanism and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad. The driving mechanism may be formed by either a single piston having a diameter being the diameter of the driving mechanism or a plurality of pistons including outermost pistons having circumferences inscribed in a circle having a diameter being the diameter of the driving mechanism.

When the driving mechanism is formed by the single piston, the diameter of the single piston is larger than the diameter of the portion of the pad. With the diameter of the single piston being larger than the diameter of the portion of the pad, the pad is pushed in its entirety by the piston so as to prevent an outer portion of the pad from being flexed by a load applied to the pad when the workpiece is punched. As a result, the workpiece can be evenly punched to provide a plurality of elements 41 having the same thickness accuracy.

When the driving mechanism is formed by the plurality of the pistons, the diameter of the circle is larger than the diameter of the portion of the pad 34. With the diameter of the circle being larger than the diameter of the portion of the pad, the pad is pushed in its entirety by the pistons so as to prevent an outer portion of the pad from being flexed by a load applied to the pad when the workpiece is punched. As a result, the workpiece can be evenly punched to provide a plurality of elements having the same thickness accuracy.

In a preferred form of the present invention, the driving mechanism comprises a plurality of pistons, the pistons have portions contacting the portion of the pad, and a total cross-sectional area of the portions of the pistons is more than 80% of a cross-sectional area of the portion of the pad.

The present inventors prepared seven pistons, and arranged one of the seven pistons with the other six pistons placed in equally spaced relation to one another around the one piston in contact with the one piston. Then, the seven pistons were activated to push the pad and punches to punch the workpiece for forming elements. Thereafter, thicknesses of the elements were measured. The measurement indicated that the elements each have the same thickness accuracy as that of each of elements formed with the total cross-sectional area being equal to the cross-sectional area of the portion of the pad. This means that even when the driving mechanism for pushing the pad is formed by the plurality of the pistons, a workpiece can be evenly punched to form a plurality of elements having the same thickness accuracy.

In a further preferred form of the present invention, the pistons are the same in cross-sectional area.

Since the respective pistons have the same cross-sectional area, the pistons are the same in weight and can be subjected to the same resistance, such that the pistons can move in the same manner. This results in the pad moving smoothly to reduce a load on a piston-actuating mechanism.

Preferably, the punches are arranged to punch the workpiece for forming plate-shaped elements for a metal belt of a belt-type continuously variable transmission, such that the elements are stacked in a peripheral direction of the belt.

A single metal belt of a belt-type continuously variable transmission uses a plurality of plate-shaped elements, and requires each of elements to have a thickness accuracy. The present invention has an advantage that punching the workpiece only once can provide a plurality of elements each having an enhanced thickness accuracy.

According to a second aspect of the present invention, there is provided a punching method comprising the steps of: providing a metal sheet and a punching apparatus, the punching apparatus comprising: a plurality of punches; a pad; and a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position, wherein the pad is supported on the driving mechanism and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad; and activating the punches to punch the sheet for forming elements for a metal belt of a belt-type continuously variable transmission.

The method has an advantage that the only one step of punching the sheet 22 can provide the elements each having a thickness accuracy for improving productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is an overall view of a workpiece-punching apparatus in one embodiment of the present invention;

FIG. 2 is a view showing a diameter of a piston and two types of diameters of a pad;

FIG. 3 is a view on an arrow 3 in FIG. 2;

FIG. 4 is a front elevation view of an element;

FIG. 5A is a view showing a punching apparatus in a comparative example and FIG. 5B is a view showing the punching apparatus in the one embodiment of the present invention;

FIG. 6 is a view showing a punching apparatus in another embodiment of the present invention in correspondence to the punching apparatus shown in FIG. 2;

FIG. 7 is a view on an arrow 7 in FIG. 6; and

FIG. 8 is a view showing a prior art punching apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a workpiece-punching apparatus 10 in one embodiment of the present invention includes a base or bolster 11, and a lower die set 13 provided on a top of the bolster 11 and defining a hydraulic cylinder 12 therein. The apparatus 10 also includes a die plate 15 disposed above the lower die set 13 with a packing plate 14 provided therebetween. The apparatus 10 further includes an upper die set 17 actuated by a driver 16 to move vertically in opposed relation to the lower die set 13. The apparatus 10 further includes a punch plate 21 disposed the upper die set 17 with a packing plate 18 provided therebetween. The apparatus 10 further includes a vertically moveable upper die pad 23 disposed below the punch plate 21 for clamping a workpiece or metal sheet 22 from thereabove.

Attached to the packing plate 18 is a guide post 24 for guiding the punch plate 21 and the upper die pad 23 to the die plate 15. A retainer 25 is attached to the packing plate 18 for limiting downward movement of the upper die pad 23.

The apparatus 10 further includes a driving mechanism formed by a single piston 31 slidably disposed in the hydraulic cylinder 12. Contained in the hydraulic cylinder 12 is an oil 26 adapted to exert a hydraulic pressure on the piston 31. The apparatus 10 further includes a pad 34 disposed on a top surface of the piston 31 and supported by the piston 31. Disposed on a top surface 33 of the pad 34 are a plurality punches (hereinafter referred to as “counter punches”) 32, as will be detailed later with reference to FIG. 2 and FIG. 3. Attached to the packing plate 18 are forming punches 35 for punching the sheet 22 from thereabove.

The piston 31 and the oil 26 cooperate to form a hydraulic mechanism 36. The piston 31 moves the pad 34 and the plurality of the counter punches 32 together between an advanced position and a retracted position.

Turning to FIGS. 2 and 3, the piston 31 has a diameter D3 and the pad 34 has a diameter D4. The pad 34 has an inner portion 34 a supporting the counter punches 32. More specifically, the inner portion 34 a of the pad 34 has the counter punches 32 on a top surface 33 a of the inner portion 34 a. The inner portion 34 a of the pad 34 has a diameter D5. The top surface 33 a of the inner portion 34 a having the diameter D5 has its circular circumference C1 circumscribing respective circumferences of six outermost ones of the counter punches 32. The diameter D3 of the piston 31 is larger than the diameter D4 of the pad 34, and the diameter D4 of the pad 34 is larger than the diameter D5 of the inner portion 34 a of the pad 34 (D3>D4>D5).

As shown in FIG. 3, the top surface 33 a of the inner portion 34 a, which has the circumference C1 circumscribing the circumferences of the six outermost counter punches 32, is adapted to bear a load through the counter punches 32 when the workpiece is punched. That is, the inner portion 34 a is a “substantial part” of the pad 34 to bear the load applied through the counter punches 32 during the punching of the workpiece, and the diameter D5 of such a “substantial part” 34 a of the pad 34 is defined as a “substantial diameter” of the pad 34. It is noted that the diameter D3 of the piston 31 is larger than this “substantial diameter” D5 of the pad 34. Although the pad 34 and the piston 31 are circular in shape when viewed in plan in this embodiment, the pad 34 and the piston 31 may have their outlines of another shape such as a quadrangular shape when viewed in plan as long as the diameter D3 of the piston 31 is larger than the “substantial diameter” D5 of the pad 34.

As shown in FIG. 4, the sheet 22 is punched to form elements 41 for a metal belt of a belt-type continuously variable transmission. The elements 41 each include a head 42, a neck 43 and a body 44. The elements 41 are stacked on one another in a peripheral direction of the belt. The elements 41 should have thickness accuracies.

A method for punching a workpiece to form the elements 41 includes steps of providing the punching apparatus 10 shown in FIG. 1 and the metal sheet 22; and activating the forming punches 35 and the counter punches 32 of the punching apparatus 10 to punch the sheet 22 to form the elements 41.

Discussion will be made as to advantages of the punching apparatus 10 in comparison with a punching apparatus in a comparative example.

Referring to FIG. 5A, the punching apparatus in the comparative example includes a piston 121 slidably disposed in a hydraulic cylinder under a hydraulic pressure, and a pad 124 provided atop the piston 121. The pad 124 has a plurality of counter punches 122 on a top surface 123 thereof. The pad 124 is moved together with the counter punches 122 by the piston 121 between an advanced position and a retracted position. The piston 121 has a diameter D6. The top surface 123 of the pad 124 has a region having a circumference circumscribing a circumference of each of outermost ones of the counter punches 122, and such a region has a diameter D7 which is defined as a “substantial diameter” of the pad 124 as in the “substantial diameter” D5 of the pad 34. The diameter D6 is smaller than the diameter D7 (D6<D7).

When the piston 121 of the punching apparatus in the comparative example moves upward, as indicated by an arrow (1), for punching a workpiece (not shown), the counter punches 122 are each subjected to a load F1. Then, the pad 124 is not deformed or flexed at its center and a vicinity of the center because the center and its vicinity are supported by the piston 121 located directly below the pad 124. However, the pad 124 is flexed at its an outer portion because the outer portion of the pad 124 is not supported by the piston 121. That is, the outer portion of the pad 124 supporting the outermost counter punches 122 is downward flexed an amount L1 on a fulcrum defined by the center of the pad 124 supporting a central one of the counter punches 122. As a result, it would be difficult for the outermost counter punches 122 to punch the workpiece to form elements having thickness accuracies.

Referring to FIG. 5B showing the punching apparatus 10, when the piston 31 moves upwardly, as indicated by an arrow (2), for punching a sheet 22 (FIG. 1), the counter punches 32 are each subjected to a load F1. Then, the pad 34 is not flexed throughout because the pad 34 is entirely supported by the piston 31. As a result, the sheet 22 is evenly punched to form plural elements 41 (FIG. 4) each having a thickness accuracy.

A punching apparatus 10 in another embodiment will be discussed with reference to FIG. 6 and FIG. 7. Components of the apparatus 10 shown in FIG. 6 and FIG. 7 corresponding to those of the apparatus shown in FIG. 1 are designated by the same reference numerals and their descriptions will be omitted.

As shown in FIG. 6 and FIG. 7, the pad 34 having the counter punches 32 disposed on the top surface 33 a of the inner portion 34 thereof is disposed on and supported by a driving mechanism formed by a plurality of pistons 37. The pad 34 is moved together with the counter punches 32 by the pistons 37 between an advanced position and a retracted position. The plurality of the pistons 37 include outermost pistons 37 having their circumferences inscribed in a circumference or circle C2 having a diameter D6, as shown in FIG. 7. It is noted that this diameter D6 of the circle C2 is defined as a diameter of the driving mechanism formed by the plurality of the pistons 37. The pad 34 has the diameter D4 and the “substantial diameter” D5. The “substantial diameter” D5 is smaller than the diameter D4. The diameter D4 is smaller than the diameter D6.

More specifically, the seven pistons 37 consist of one piston 37 and six (outermost) pistons 37 equally spaced from one another and arranged around the one piston 37 in contact with the one piston 37. The circle C2 circumscribes the respective circumferences of the six outermost pistons 37. The seven pistons 37 are the same in cross-sectional area. The “substantial diameter” D5 of the pad 34 is the diameter of the inner portion 34 a of the pad 34, as discussed above, and the inner portion 34 a of the pad 34 has a cross-sectional area A1. The seven pistons 37 have portions supporting the inner portion 34 a in contact with the inner portion 34 a and a total cross-sectional area A2 of such supporting portions of the pistons 37 is indicated by hatching.

The pad 34 is moved by the pistons 37 to punch a workpiece to form elements 41 (FIG. 4). As a result, it has been found that each of the elements 41 obtained with the total cross-sectional area A2 set to be more than 80% of the cross-sectional area A1 has the same thickness accuracy as that of each of elements 41 obtained with the total cross-sectional area A2 set to be equal to the cross-sectional area A1.

In summary, the punching apparatus 10 according to the present invention includes the plurality of the counter punches 32 for punching a workpiece, and the pad 34 with the counter punches 32 carried on the top surface 33 a of the inner portion 34 a of the pad 34. The apparatus 10 further includes the driving mechanism for moving the pad 34 and the punches 32 together between the advanced position and the retracted position. The driving mechanism is formed by either the single piston 31 or the plurality of the pistons 37. When the driving mechanism is formed by the single piston 31 shown in FIG. 2, the diameter D3 of the single piston 31 is larger than the diameter D5 of the inner portion 34 a (“substantial diameter” D5 of the pad 34). When the driving mechanism is formed by the plurality of the pistons 37, the diameter D6 of the circle C2 circumscribing the circumferences of the outermost ones of the pistons 37 is larger than the “substantial diameter” D5 of the pad 34.

With the diameter D3 being larger than the “substantial diameter” D5, the pad 34 is pushed in its entirety by the piston 31 so as to prevent an outer portion of the pad 34 from being flexed by a load applied to the pad 34 when the workpiece is punched. As a result, the workpiece can be evenly punched to provide a plurality of elements 41 having the same thickness accuracy.

With the diameter D6 being larger than the “substantial diameter” D5, the pad 34 is pushed in its entirety by the pistons 37 so as to prevent an outer portion of the pad 34 from being flexed by a load applied to the pad 34 when the workpiece is punched. As a result, the workpiece can be evenly punched to provide a plurality of elements 41 having the same thickness accuracy.

When the plurality of the pistons 37 pushes the pad 34, as shown in FIG. 7, the total cross-sectional area A2 of the supporting portions of the pistons which support the inner portion 34 a of the pad 34 is set to be more than 80% of the area A1 of the top surface 33 a of the portion 34 a of the pad 34.

The plurality of the pistons 37 pushes the pad 34 to punch the workpiece to form elements with the total cross-sectional area A2 being more than 80% of the area A1. It has been found that the elements each have the same thickness accuracy as that of each of elements formed with the total cross-sectional area A2 being equal to the area A1. This means that even when the driving mechanism for pushing the pad 34 is formed by the plurality of the pistons 37, a workpiece can be evenly punched to form a plurality of elements having the same thickness accuracy.

The plurality of the pistons 37 is the same in cross-sectional area.

Since the respective pistons 37 have the same cross-sectional area as that of one another, the pistons 37 are the same in weight and can be subjected to the same resistance, such that the pistons 37 can move in the same manner. This results in the pad 34 moving smoothly to reduce a load on a piston-actuating mechanism.

The plurality of the elements 41 is plate-shaped as shown in FIG. 4. The elements 41 are used in a metal belt of a belt-type continuously variable transmission. More specifically, the elements 41 are stacked on one another in a peripheral direction of the belt.

A single metal belt of a belt-type continuously variable transmission uses a plurality of plate-shaped elements, and requires each of elements to have thickness accuracy. The present invention has an advantage that punching a workpiece only once can provide a plurality of elements each having enhanced thickness accuracy.

The present invention provides a method for using the punching apparatus shown in FIG. 1 for punching a workpiece to form elements for a metal belt of a belt-type continuously variable transmission. The method includes providing the punching apparatus 10 and a metal sheet 22, and activating the counter punches 32 so as to punch the metal sheet 22 for forming elements 41 (shown in FIG. 4). The only one step of punching the sheet 22 can provide the elements 41 each having thickness accuracy for improving productivity.

A punching technique according to the present invention may be used for punching a workpiece to form elements of other shapes for a component other than the metal belt of the belt-type continuously variable transmission if these elements are required to have thicknesses accuracy.

The present invention is suitable for forming elements for a metal belt of a belt-type continuously variable transmission.

Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 

What is claimed is:
 1. A punching apparatus comprising: a plurality of punches for punching a workpiece; a pad; and a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position, wherein the pad is supported on the driving mechanism and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad.
 2. The apparatus of claim 1, wherein the driving mechanism comprises a single piston having a diameter being the diameter of the driving mechanism.
 3. The apparatus of claim 1, wherein the driving mechanism comprises a plurality of pistons including outermost pistons having circumferences inscribed in a circle having a diameter being the diameter of the driving mechanism.
 4. The apparatus of claim 1, wherein the driving mechanism comprises a plurality of pistons, the pistons have portions contacting the portion of the pad, and a total cross-sectional area of the portions of the pistons is more than 80% of a cross-sectional area of the portion of the pad.
 5. The apparatus of claim 4, wherein the pistons are the same in cross-sectional area.
 6. The apparatus of claim 1, wherein the punches are arranged to punch the workpiece for forming plate-shaped elements for a metal belt of a belt-type continuously variable transmission, such that the elements are stacked in a peripheral direction of the belt.
 7. A punching method comprising the steps of: (i) providing a metal sheet and a punching apparatus, the punching apparatus comprising: a plurality of punches; a pad; and a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position, wherein the driving mechanism supports the pad and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad; and (ii) activating the punches to punch the sheet for forming elements for a metal belt of a belt-type continuously variable transmission. 